The organic EL panel is a self-emission panel provided with an organic EL element as a light-emitting element. For example, the organic EL panel is used for display screens of mobile phones, monitor screens of electronic devices in automobiles or for family use, and information display screens of PCs and TVs. The organic EL panel is also used for various types of display devices such as advertising light-emitting panels, various types of light sources in scanners and printers, and illuminating devices such as generally-used lighting systems and back-lighting of LCDs. Further, the organic EL panel is available for various applications and devices such as optical communication devices using the photoelectric conversion function.
Since the light-emission properties of organic EL elements deteriorate when exposed to moisture, etc., a sealing structure for separating the organic EL element from the atmosphere is inevitable in order to use an organic EL panel for a long time in a stable condition. As one example for sealing the organic EL element, a hollow-sealed structure is known in which a sealing substrate is bonded to a panel substrate having the organic EL element to form a sealing space for housing the organic EL element and to place a drying agent in the sealing space.
FIG. 1 is a schematic view showing a conventional hollow-sealed structure having the above-mentioned sealing space of the organic EL panel. FIG. 1(a) is a plan view, FIG. 1(b) is a sectional view taken along line A-A of FIG. 1(a), and FIG. 1(c) is a sectional view taken along line B-B of FIG. 1(a). The organic EL element, being a light-emitting element is formed on a panel substrate J1 (not shown). A sealing substrate J2 is bonded to the panel substrate J1 through an adhesive layer J3 to make a sealing space is for housing the light-emitting element. The sealing substrate J2 has a concave portion J4 to make the sealing space Js. On the inner surface of the concave portion J4, a drying agent J5 is placed to absorb the moisture in the sealing space Js. Further, a thick rib J6 is formed on the concave portion 14 of the sealing substrate J2 in order to reinforce the sealing substrate 12 (see the following patent literature reference 1).